Java Map MCQs with answers Page - 2

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Q. Which method checks whether a Map contains a specific key?

  • (A) hasKey()
  • (B) containsKey()
  • (C) keyExists()
  • (D) findKey()

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Q. Which Map implementation allows one null key and multiple null values?

  • (A) HashMap
  • (B) TreeMap
  • (C) Hashtable
  • (D) EnumMap

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Q. What does `entrySet()` return in a Map?

  • (A) List of keys
  • (B) List of values
  • (C) Set of key-value pairs
  • (D) List of keys and values separately

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Q. Which class is used to make a Map thread-safe without using Hashtable?

  • (A) Collections.synchronizedMap()
  • (B) ThreadSafeMap
  • (C) ConcurrentMap
  • (D) ConcurrentHashMap

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Q. Which Map implementation is best for high-concurrency environments?

  • (A) HashMap
  • (B) TreeMap
  • (C) ConcurrentHashMap
  • (D) LinkedHashMap

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Q. What is the return type of `putIfAbsent()` in ConcurrentHashMap?

  • (A) boolean
  • (B) void
  • (C) int
  • (D) V

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Q. Which Map is sorted by its keys?

  • (A) HashMap
  • (B) TreeMap
  • (C) LinkedHashMap
  • (D) Hashtable

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Q. Which Map implementation does NOT allow null keys or values?

  • (A) HashMap
  • (B) LinkedHashMap
  • (C) Hashtable
  • (D) TreeMap

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Q. Which interface defines `getOrDefault()` method in Java 8?

  • (A) Collection
  • (B) List
  • (C) Map
  • (D) Set

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Q. Which method can replace an existing value in a Map only if it is currently mapped to a given value?

  • (A) putIfPresent()
  • (B) replace()
  • (C) override()
  • (D) update()

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